42 BULLETIN 801, XT. S. DEPARTMENT OE AGRICULTURE. 
Slow-burning construction— sometimes called ;; mill construc- 
tion " — consists of substantial masonry walls and heavy timber fram- 
ing with thick and closely laid floors and roof, all arranged so that no 
concealed spaces, or pockets, are formed. Although this may be con- 
sidered a brief definition, there are a number of essential details 
which should be adhered to if the building is to be worthy of its 
name. For example, timbers which are carried at the end by walls 
should be supported there in such manner that failure and falling 
of the timber would not damage the wall. The value of proper con- 
struction, in this particular, is shown by the photograph in Plate 
XXII, figure 1, in which case heavy timbers resting on corbels have 
fallen without damage to the wall though an entire compartment was 
consumed. It is true that the first requisite is control of the fire, 
but a close second consideration is that damage be restricted and re- 
pair made easy. 
Some general features of slow-burning construction as embodied 
in a well-designed warehouse are shown in Plate XXII. figure '2. 
The cast-iron post cap gives a good connection between the post 
and timbers. 
DIVISION FIRE WALLS. 
Division fire walls should be of the same material as that specified 
for such walls of the fire-resistive construction and the general re- 
quirements are the same. There is, however, one factor to be con- 
sidered here that is of greater importance than it is in the case of 
fire-resistive construction — that is. stability against overturning or 
buckling from heat. In the construction having reinforced con- 
crete floors and roof, these supply a rigid tie to the wall; but in 
slow-burning construction, the wall must stand upon its own merits 
and must sustain the shock of falling timbers and goods. Sufficient 
stability usually is supplied by the thickness and other proportions 
specified previously for brick walls of the bearing type. 
An excellent fire wall is shown in Plate XXIII. The compart- 
ment was full of cotton, which was entirely consumed. Xote'that 
the heavy tapering buttresses held this unusually long wall against 
the buckling and overturning which a severe fire frequently causes. 1 
1 The resistance to buckling^ of the long, wall under the test of hear may 
be supplied by cross walls or buttresses instead of the additional thickness 
previously described. Buttresses should be placed at intervals not exceeding 
100 feet and preferably of 50 feet. This type of buttress (shown on PL XXVI, 
fig. 3) should be built with and into the wall and not merely against it. The 
combination of vertical surfaces and off-sets should be such as to be equivalent 
to a tapering buttress (indicated by the heavy dotted line) having a pro- 
jection at the first floor of one-tenih the height of the wall; the face (or 
thickness measured parallel to the wall) should be 24 inches, If concrete is 
